Pale shader for alternating current magnets



Dec. 22, 1931. P. TROMBETTA 1,837,923

POLE SHADER FOR ALTERNATING CURRENT MAGNETS Filed July 28, 1950 Fig.

Invenior: Pan iLoT'PombeUla, 9 W

H is Attorney.

Pateiitecl Dec. 22, 1931 UNITED STATES PATENT OFFICE PANFILO TBOMTBETTA, OF MILWAUKEE, WISCONSIN, ASSIGNOB. TO GENERAL ELECTBIC COMPANY, A. CORPORATION OF NEW YORK PALE SHADEB FCB ALTEBNATING CURRENT MAGNETS Application filed m 28, 1930. Serial 110. 471,307.

My invention relates to alternatingcu'rrent electromagnets and more particularly to the shading coils used therewith.

In alternating current electromagnets humming or chattering of the armature 1s one of the difficulties which must be over come. The means for accomplishing this result is the shading coil which is a short clrcuitod coil placed in or near the pole face of the electromagnet. The reversal of the flux through the electroma-gnet and its consequent building up and collapsing induces an electromotive force in the shading coil which results in the production of a flux which is out of phase with the main flux. The result is that as the main flux passes through a zero value the auxiliary flux which is produced by the shading coil increases to a maximum value so that there is at all times a pull exerted upon the armature which materially reduces or eliminates the chattering which would normally result.

It is well known that usually in the present forms of shading coils the out-of-phase flux which is produced thereby is small and does not result in practically noiseless operation. Increasing the number of turns in the shading coil does not solve the difiiculty because although the induced electromotive force produced therein is increased the flux is not increased to-any great extent due to the increase of the reactance of the shading coil which limits the out-of-phase current and hence the resulting out-of-phase flux whlch R5 maintains the armature in close contact with the electromagnet during periods of low main flux. Therefore, for a given magnet frame and agiven exciting coil the greatest possible noiseless pull is practically fixed. Since this pull is small, when a large noiseless pull is desired unusually large and expensive magnet frames are required.

Hence the principal object of my invention is the provision of an alternating current electromagnet which is inexpensive and which will practically eliminate chattering.

Specifically it is the object of my invention to provide an alternating current electromagnet in which the shading coils produce an out-of-phase flux which is greatly increased over usual present forms but without increasing to any great extent the reactance of the shading coil. 1

Other objects will appear hereinafter;

In the preferred embodiment of my invention I provide an electromagnet having a plurality of legs provided with faces having slots therein. The shading coils are placed in these slots and connected in series to cause an additive efi'ect of'the resulting induced voltage. One of the poles is cut back or made shorter than the other, or others, the invention being applicable to two or three pole electromagnets, which results in increasing the induced voltage in the-coil without increasing its reactance in the same ratio, therebv resulting in an increased, out-of-W phase flux due to the increase of induced current in the shading coil.

In the accompanying drawings Fig. 1 shows a sideview of one form of my invention: Fig. 2 shows the electromagnet and shading coil details of Fig. 1; Fig. 3 is a modification of my invention and Fig. 4 shows the electromagnet and shading coil details thereof: Fig. 5 is still another modification of my invention. I

In Figs. 1 and 2 of the drawings, the electromagnet 10 is provided with slots 11 and 12. Q Shading coils-13 and 14 are placed in the slots 11 and 12 and connected as shown at the rear of the electromagnet. The electromagnet is secured to a base 15 and 'is provided with a pivoted armature =16 cooperating therewith. It will be noted that a gap is provi ded between the armature 16 and the lower leg of the electromagnet when the armature is in closed position. Mounted on one leg of the electromagnet '10 is the exciting coil 17 for energizing the electromagnet. -A stop 18 is provided for the armature.

In operation, when exciting current passes through the coil 17 an alternating main flux results in the electromagnet 10which results in moving the armature 16 into contact with the up er leg of the electromagnet.

As the flux collapses and builds up in the electromagnet 10 it induces in the shading. coils 13 and 14 which are connected in series a voltage which is twice the voltage which would have been induced in only the one coil. This induced electromotive force results in a current through the coils in a direction to cause a large out-of-phase flux for maintain ing the armature closed during periods when the main flux passes through zero value. The inductance of the local circuits of the coils 13 and 14, more particularly of the portions of the shading coils which are placed in the slots,

depends upon the reluctance of the path through which the out-of-phase flu); must pass. It will be seen that in the upper'leg of the electromagnet practically a closed mag netic circuit is provided in the electromagnet and the armature 16 with a resulting high reactance of coil 13. However, in the lower leg a gap between the lower leg and the armature results in an increase of the reluctance of the magnetic path for the local circuit of the coil 14. Hence the reactance of the lower coil 14 is far less than that of the upper coil 13 but due to the fact that the same main flux cuts the lower coil 14 as cuts the upper coil 13 equal voltages will be produced in both coils. The result is that an electromotive force twice that which would be produced in one coil is produced but the reactance of the coil is increased in a much smaller ratio. This, of course, results in a larger flow of current through the combined coils and a greater outof-phase flux to hold the armature against its tendency to chatter.

In Figs. 3 and 4 is shown an E-shaped electromagnet making use of the same principles as those used in the form shown in Figs. 1 and 2. In this form the middle leg is cut back with the same result produced in the U- shaped coil. that is of increasing the induced voltage inthe shading coil while maintaining the reactance at a relatively low value. In the form shown in Figs. 3 and 4 the electromagnet 20 is mounted on a base 21 and provided with a pivoted armature 22. The exciting coil 23 which is mounted upon the middle leg of the electromagnet furnishes the exciting current to produce the main flux in the magnet. The electromagnet 20 is provid ed with the slots 24, 25 and 26 in the pole faces in which are mounted the shading coils 27 and 28. The coils are connected in series as can be clearly seen in the drawings so that the voltages induced therein have an additive effect in a manner similar to that in the form shown in Figs. 1 and 2. The total flux passes through the middle leg and divides between the two outer legs of the electromagnet so that as the' flux collapses and builds up the portions of the coils, 27 and 28 which lie in the slots 24 and 26 and the portions of these coils lying on the outside of the middle leg are cut by the flux to produce the induced voltages therein. The portions of the coils lying in the slot 25 of the middle leg are out by very little or no flux so that practically no induced voltage results in this portion of the coils. The middle leg of the electromagnet iscut back to provide a gap between it and the armature to reduce the reactance, as explained above, of the portion of the shading coils mounted thereon. That is, the reluctance of the magnetic path of the local circuits of the coils adjacent the outside of the middle leg is much greater than the reluctance of the magnetic path of the local circuits of the coils in the slots in the outside legs. The result is that the induced voltage in the shading coils is increased in a greater ratio than the reactance of the coil. This is explained by the fact that the induced vol tages in each coil are practically the same being cut by the same flux and are added whereas the reactance does not increase in the same ratio due to the difference in the reluctance of the magnetic paths of the local circuits of the shading coils. This results in a larger out-of-phase 'flux for maintaining the armature closed during operation of the electromagnet.

' In Fig. 5 an electromagnet 30 is provided with the slots 31,32. 33 and 34. Mounted in these slots are the shading coils 35. 36, 37 and 38. The modification shown in Fig. 5 may be comparable to two of the forms shown in Fig. 1 adjacent each other. The middle pole of electromagnet 30 is cut back similar to the form shown in Figs. 3 and 4. The same operati on takes place with this form of electroma net.

Hence it will be seen that I have provided a shading coil which is equally applicable to small and large electromagnets and which provides a greater out-of-phase flux than is normally provided thus producing a more nearly noiseless operation of the electromagnet. This result is due to the ability to increase the induced electromotive force without increasing in proportion the reactance of the shading coil.

The embodiment of the invention illustrated and described herein has been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use, and I, therefore, aim to cover by the appended claims all of the modifications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An alternating current electromagnet having an armature and a pluralityof poles, an exciting coil for said electromagnetfor producing a main flux therein, shading coils mounted in the faces of said poles for produci'ng an out-of-phase flux and connected in series whereby the induced voltages in said coils are added, one of said poles being provided with a gap between it and the armature to effect a decrease in the reactance which said shading coils would normally have tov materially increase the out-of-phase flux..

2. An alternating current electromagnet provided with a plurality of poles and having an armature, an exciting, coil to produce a main flux in said magnet, slots in the faces of said poles, shading coils mounted in said slots and connected in series whereby the induced voltages in said coils are'added, one of said poles being cut back from said armature to effect a decrease in the reactance which said coils would normally have, whereby the resulting out-of-phaseflux is materialy increased.

3. An alternating current electromagnet provided with a plurality of poles, pole shading windings placed in the pole faces and connected to cause additive effect of the induced voltage in said shading windings, and an an 'mature cooperating with said electromagnet,

one of said poles being shorter than the others to provide a gap between said armature and the pole face of said one pole.

4. An alternating current electromagnet provided with a plurality of poles, slots in the fa es of said poles, shading coils placed in said slots and connected in series to cause an additive eflect of the induced voltages therein, an armature cooperating with said poles, one of said poles being shorter than the others to provide a gap between said armature and the pole face thereof.

5. An alternating current electromagnet of U-shape each leg being provided with a face with a slot therein, shading coils mounted in each slot and connected in series to produce additive effect of the induced voltages in said coils, an armature cooperating with the legs of said electromagnet one of said legs being shorter than the other to provide a gap between its face and said armature.

6. An alternating current electromagnet of U-shape. each leg provided with a pole face withv a slot near the inner edge of each face, a shading coil in each slot, said coils being connected in series to cause the induced voltages therein to be added, an armature coopcrating with the legs of said magnet, one of said legs being shorter than the other to provide a gap between said armature and said leg whereby the reactance which said shading coils would normally have is materially decreased.

'ng(provided with a slot 

